Automatic Landing of a Vehicle with Sloshing Tanks

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Flixan, Flight Vehicle Modeling, Control Design and Analysis Program

Flixan® is a Windows® based program for modeling flight vehicle dynamics and for analyzing and designing flight control systems. It generates flight vehicle and spacecraft dynamic models for simulations, control analysis and design, analyzes system stability, performance, and robustness to uncertainties. It was motivated by the necessity of rapidly generating and analyzing dynamic models for a variety of vehicles concepts and complexity. It is a collection of modeling and analysis programs and utilities that can accommodate a wide range of flight vehicle concepts, such as, aircraft, gliders, spacecraft, space shuttles, space stations, launch vehicles, rocket planes, missiles, reentry vehicles, etc.

The complexity of the model is defined by the user, and many examples are included for reference and details. We typically begin with simple rigid body models for preliminary analysis which are gradually increased in complexity to include high order dynamics with many structural modes, aero-elasticity, propellant sloshing, actuator and sensor dynamics, tail-wags-dog dynamics, hinge-moments, wind disturbances, etc. The vehicle configuration and complexity is defined in the input data. The model may include any number of thruster engines, reaction control jets, aerosurfaces, control moment gyros, reaction wheels, bending modes, propellant sloshing tanks, rate gyros, accelerometers, etc. The program places a great emphasis in the dynamic modeling of structural flexibility in both atmospheric vehicles and space structures, the methodology of selecting structural modes from finite element models, and the modeling of liquid sloshing in propellant tanks, including many examples. The quality of our product is successfully tested using real flight vehicles, such as the Space Shuttle, Space Station, etc.

The Flixan® program also includes utilities for other functions, such as, implementing flight control laws, combining, manipulating, and discretizing systems. It also includes utilities for control design, early evaluation of vehicle concepts by static analysis, trimming the effectors and analyzing static performance and maneuverability from vehicle data without dynamic models. There are also programs for modeling flexible structures, selecting flex modes, modeling and analyzing robustness to parameter uncertainties, modeling hydraulic and electro-mechanical actuators, a program for combining various types of effectors, etc. The models are either analyzed within Flixan® or they can be exported to Matlab® for further analysis.